FERTILISERS FOR WAREPA SOILS

New Zealand Journal of Agriculture, Volume 95, Issue 2, 15 August 1957, Page 125

FERTILISERS FOR WAREPA SOILS

Recent Research Work

kyjOST of the foothill soils of Berwick, •’I Maungatua, Woodside, Outram, and north Taieri areas, portions of the coastal hills fro m north Taieri to Taieri Mouth, and the St. Clair-Blackhead areas fall into the Warepa class, and many of the downs soils of South Otago are of a similar type. Over the last 7 years a great deal of experimental work has been done with the co-operation of local farmers and valuable information on the fertiliser requirements of these soils has been accumulated.

VALUE OF MOLYBDENUM

IN 1949 Mr. J. O. H Tripp of Outram obtained excellent re-

suits from topdressing strips with basic slag at 2cwt. and ' 4cwt. per acre, though on the same nfe-ph field, which was predominantly brown- “/t- 4 ? top with some very poor clovers, - E there was no response to superphos- •*" phate at up to 1 ton per acre. This led to a revival of interest in molybdenum, which was found to be present in basic slag and observational molybdenum trials, confirmed the value of this trace element.

In September 1951 a replicated mowing trial was laid down in an adjacent field to compare the following treatments: Superphosphate (3cwt.); superphosphate plus sodium molybdate (j-oz.); superphosphate plus sodium molybdate (2|oz.); basic slag (3cwt.) and superphosphate plus ammonium vanadate (lib.).

In the first season both rates of molybdenum in combination with superphosphate were equally effective and showed significantly higher yields than any other treatment. Superphosphate and basic slag were not reapplied in 1952, and in the 1952-53 season molybdenum had little effect, probably owing to shortage of phosphate or sulphur. In 1953 (and annually since then) superphosphate and basic slag were reapplied with an over-all dressing of muriate of potash at lcwt. per acre. In the 1953-54 season molybdenum plots again showed a marked yield advantage, but yields from the joz. application had begun to fall off in comparison with those of the 2|oz. rate. Nevertheless, 4 years after the start of the trial the |oz. of sodium molybdate was still having a marked influence on yield.

FAILURE OF BASIC SLAG

At the instigation of E. B. Davies, Senior Chemist, Rukuhia Soil Research Station, who had been responsible for the original

experiments with molybdenum, sodium tungstate at lib. per acre was applied to one replication of the trial in September 1953. A response to tungsten almost equal to that of molybdenum very soon became evident on plots which had already been treated with superphosphate and superphosphate plus vanadium, but there was no response where basic slag had previously been applied. Whereas superphosphate contains sulphur, basic slag does not, and the failure of the basic slag-treated plot to respond to tungsten pointed to the possibility of a sulphur deficiency. Consequently in September 1955 calcium sulphate at l|cwt. per acre was applied to half of each basic slag plot. A very definite response to the calcium sulphate treatment followed. The occurrence of both phosphate and sulphate deficiency on this Warepa soil was confirmed in an adjacent trial, where the yield from calcium sulphate plus double phosphate was superior to that from either double superphosphate or calcium sulphate alone. These findings could, in part at least, explain why some farmers 5 on this foothill country have had good initial responses to basic slag followed by disappointing results

from its continued use. They are also important at present, when aerial application of double superphosphate is being considered by some farmers. Double superphosphate, like basic slag, does not contain sulphur and results from its use are likely to be disappointing.

REPEAT DRESSINGS OF MOLYBDENUM

Information on the necessity for repeat applications of molybdenum was also required and in September 1955, 4 years after the original molybdenum

treatments were applied, repeat applications were made on half plots. Responses to these repeat dressings became apparent on the ioz. per acre treatments within 1 month, and by January 1956 were showing slightly on the 2Joz. per acre plots, indicating the desirability of applying further molybdenum after 4 years.

APPLICATION OF RESULTS

Warepa soils respond to applications of phosphate, sulphate, molybdate, tungstate, and lime. From the results of these accurately measured trials, numerous

observational trials, and farmers’ experiences the following general recommendations can be made for the Warepa soils: —

1. Molybdenum should be applied as early as possible in any cropping or pasture-improvement programme and thereafter at approximately 4-year intervals. Rates in excess of 2|oz. per acre should not be necessary. 2. Superphosphate, which supplies both phosphate and sulphate, should be applied with all crops and annual applications should be made to pastures. Good results have been given by 3cwt. per acre, but on some areas heavier applications may be payable. Autumn application promotes out-of-season pasture production and is to be preferred to spring treatment. 3. Phosphates which do not contain sulphur, such as basic slag and double phosphate, should not be used. 4. Provided molybdenum is used, liming at 1 ton per acre initially with moderate maintenance dressings equivalent to 3cwt. per acre per annum should generally be adequate. 5. Tungsten (lib. per acre of sodium tungstate) has given very definite responses, the indication being that it is a substitute for molybdenum but is less efficient. It has no effect where molybdenum, even at a much lower rate, has already been applied.

—S. M. J. STOCKDILI